Air filters positioned within or as part of an air intake system for an engine provide filtered air for the engine. Air filters can extract dust, dirt, and other air borne materials from an engine's air intake system so that air borne material does not collect in the engine and degrade engine performance and operation. However, air borne material can collect within the air filter over time such that the air filter restricts air flow into the engine. The air flow restriction from the air filter can increase engine pumping work and reduce vehicle fuel economy.
Attempts to diagnose air filter restriction include monitoring differential pressure across the air filter during engine operation. One example approach is shown by Bauerle in U.S. Pat. No. 7,444,234. Therein, a barometric pressure is either calculated at engine-off conditions based on output from a manifold absolute pressure (MAP) sensor or during part-throttle engine operating conditions based on one or more of an existing mass air flow, MAP, engine intake throttle position, and engine speed. Further, pressure downstream of the air filter and upstream of the engine intake throttle is estimated based on output from the MAP sensor during high intake air flow conditions such as wide open throttle (WOT) conditions. The difference between barometric pressure (e.g., upstream of the air filter) and pressure downstream of the air filter (e.g., upstream of engine intake throttle) is calculated. If the difference is greater than a threshold, the air filter is determined to be plugged.
The inventors herein have recognized a potential issue with the above approach. For example, air filter diagnosis depends on the engine being operational and intake air flowing into the engine. In a hybrid vehicle, however, the engine may operate for shorter durations. Thus, the air filter diagnostic may not be performed regularly, and further, when performed, the diagnostic may take a longer time for completion. As such, the vehicle may operate with a clogged or blocked air filter for extended periods of time if the air filter diagnostic is not performed or remains incomplete. Further still, restriction of the air filter may reduce air flow into the intake causing a richer air-fuel mixture in the engine, which can foul spark plugs and affect ignition timings.
The inventors herein have recognized the above issue and have developed approaches to at least partially address this issue. In one example, a method for an engine in a hybrid vehicle comprises, during an engine-off condition, indicating degradation of an air filter based on a comparison of atmospheric pressure and a pressure in an intake manifold of the engine, the pressure in the intake manifold being a negative pressure produced via a pump coupled to an evaporative emissions system of the engine. In this way, the air filter may be diagnosed for degradation even during engine-off conditions.
As one example, a hybrid vehicle may include a fuel combusting engine and a motor drawing energy from an energy storage device, e.g. a battery. The vehicle may also include an evaporative emissions system coupled to an evaporative leak check module (ELCM), the ELCM including a pump. When the vehicle is powered off or when the vehicle is propelled primarily by motor torque, a diagnostic to test an air filter in an intake passage of the fuel combusting engine may be triggered. The diagnostic may include activating the pump in the ELCM to evacuate the intake manifold. Specifically, a canister purge valve and an intake throttle may be opened such that operating the pump draws air from an intake manifold and the intake passage downstream of the air filter through the canister purge valve. As such, a negative pressure may be produced downstream of the air filter. Degradation of the air filter may be indicated based on a comparison of barometric pressure upstream of the air filter and the pressure in the intake manifold after operating the pump for a specific duration. Further, in some cases, a remaining lifetime of the air filter may be predicted based on the comparison of barometric pressure and intake manifold pressure.
In this way, an air filter coupled in an engine of a hybrid vehicle may be diagnosed for restriction. Specifically, a state of the air filter may be analyzed even when the engine is deactivated. Further still, the air filter may be assessed for clogging without relying on engine vacuum. A pressure differential may be produced across the air filter by operating a pump included in an ELCM to diagnose the air filter for restriction. By diagnosing restriction of the air filter and predicting a remaining lifetime of the air filter, a vehicle operator may be alerted of a degrading air filter condition and prompted to take corrective actions (such as replacing the air filter) before the air filter becomes fully restricted. Thus, a blocked air filter may be detected earlier allowing the engine to operate more efficiently. As such, fuel economy may be enhanced and engine operation may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.